1. Field of the Invention
The present invention relates to a projection display device for projecting an image on an imager on a screen or the like, and in particular, is preferably used for a type of a projection display device in which a projection light enters a projected plane from a direction oblique to the projected plane at a wider spread angle by reflecting the projection light by a mirror.
2. Description of the Related Art
Conventional projection display devices (hereafter, referred to as “projectors”) have such an arrangement that, as shown in, for example, FIG. 7, projection light from an optical engine is projected on a screen by a projection optical system. In this case, widening of a distance between the projector and the screen allows displaying of a large-sized image on the screen. On the other hand, people and things are not allowed to stand in a space between the projector and the screen, thereby causing a problem that the space is wasted.
The problem may be resolved by, for example, reducing a throw distance of the projector. However, for the reduced throw distance, a diameter of a projection lens needs to be increased and a focal distance needs to be decreased (a curvature of the projection lens is increased), and another problem such as the projection lens becomes gigantic will be caused.
On the other hand, a spread angle of a projection light can be widened by reflecting the projection light from the projection optical system by an aspherical mirror. According to this method, the projection light enters from a direction oblique to the screen plane as shown in FIGS. 8A and 8B, and therefore, a space needed to secure traveling of the projection light is restricted. Further, widening of the spread angle of the projection light (hereafter, this is referred to as a “wider angle” of the projection light) is achieved by the aspherical mirror, and therefore, the wider angle can be obtained by a comparatively smaller aspherical mirror without using the gigantic projection lens as mentioned above. Accordingly, increase in size and cost in the projectors can be suppressed.
FIG. 9 illustrates an example of an arrangement of an optical system in a case where a projection light from a projection optical system is reflected by an aspherical mirror.
In FIG. 9, reference number 10 denotes an optical engine, reference number 40 denotes a projection optical system, and reference number 50 denotes an aspherical mirror. The optical engine 10 includes an optical system from a light source 11 to a dichroic prism 28, and a suction fan 30 for cooling the light source 11. The dashed line in the figure shows an outline of the optical engine 10.
The light source 11 comprises a lamp and a reflector, and emits approximately parallel light to a fly-eye integrator 12. The fly-eye integrator 12 comprises first and second integrators having groups of lenses, the lenses being arranged like a fly-eye, and gives a lens function to the light emitted from the light source 11 so that uniformity of light distribution is obtained when the light emit to liquid crystal panels 18, 21 and 27. In other words, the light transmitted through each lens of the groups of the lenses disposed like the fly-eye are respectively entered to the liquid crystal panels 18, 21 and 27 with a spread corresponding to an aspect ratio of the liquid crystal panels.
A PBS (polarized beam splitter) array 13 has a plurality of PBSs and ½ wavelength plates arranged like an array, and arranges a direction of polarization of the light entered from the fly-eye integrator 12 in one direction. A condenser lens 14 converges the light entered from the PBS array 13.
A dichroic mirror 15 reflects, for example, only light in a blue wavelength band (hereafter, referred to as “B-light”), among the light entered from the condenser lens 14, while light in a red wavelength band (hereafter, referred to as “R-light”) and light in a green wavelength band (hereafter, referred to as “G-light”) are transmitted. A mirror 16 reflects the B-light reflected by the dichroic mirror 15 to enter the B-light to a condenser lens 17. The condenser lens 17 gives a lens function to the B-light so that the B-light is entered to the liquid crystal panel 18 in a state of approximately parallel light. The liquid crystal panel 18 is driven in response to an image signal for a blue color and modulates the B-light in response to a driven state of the liquid crystal panel 18. The B-light transmitted through the condenser lens 17 is entered to the liquid crystal panel 18 via a polarizer (not shown).
A dichroic mirror 19 reflects, for example, only the G-light of the R-light and G-light transmitted through the dichroic mirror 15. A condenser lens 20 gives a lens function to the G-light so that the G-light is entered to the liquid crystal panel 21 in a state of approximately parallel light. The liquid crystal panel 21 is driven in response to an image signal for a green color and modulates the G-light in response to a driven state of the liquid crystal panel 21. The G-light transmitted through the condenser lens 20 is entered to the liquid crystal panel 21 via a polarizer (not shown).
Relay lenses 22 and 24 give a lens function to the R-light so that an incident state of the R-light with regard to the liquid crystal panel 27 becomes identical with incident states of the B-light and G-light with regard to the liquid crystal panels 18 and 21. Mirrors 23 and 25 change a light path of the R-light so that the R-light transmitted through the dichroic mirror 19 is guided to the liquid crystal panel 27. A condenser lens 26 gives a lens function to the R-light so that the R-light is entered to the liquid crystal panel 27 in a state of approximately parallel light. The liquid crystal panel 27 is driven in response to an image signal for a red color and modulates the R-light in response to a driven state of the liquid crystal panel 27. The R-light transmitted through the condenser lens 26 is entered to the liquid crystal panel 27 via a polarizer (not shown).
A dichroic prism 28 synthesizes the B-light, G-light, and R-light being modulated by the liquid crystal panels 18, 21 and 27, and enters the synthesized light to the projection optical system 40. The projection optical system 40 includes a group of lenses for image formation of the projection light on the projected plane. The aspherical mirror 50 widens the projection light entered from the projection optical system 40 and projects it on the projected plane.
With an arrangement in which the projection light from the projection optical system is reflected by the aspherical mirror, as shown in FIGS. 8A and 8B, the shorter a distance (h0) from the screen to a projection light emitting position is, the smaller the space for the projection light traveling is, and then, a possibility that the projection light is blocked by obstacles or the like is reduced. With the arrangement shown in FIG. 8A being used, when a person explains referring to images projected on the screen, the shorter the distance h0 is, the closer the person can stand to the screen, thereby presenting his/her explanations in a smooth manner. Similarly, when the arrangement shown in FIG. 8B is used, the shorter the distance (h0), the lower the possibility that the projection light is blocked by people around a desk or things placed on the desk, thereby providing higher operability or usability for user.
In this way, the projector of this type reflects light from the projection optical system 40 by the aspherical mirror 50 and projects the light on the screen, therefore, reduction in size in a direction of an optical axis in the projection optical system 40 poses a problem.
However, in the example of the arrangement shown in FIG. 9, since the suction fan 30 is disposed on a side of a wall surface of a holding mechanism, desk, or the like as shown in FIG. 10, it is necessary to provide a distance (h1) between the optical engine 10 and the wall surface to secure suction by the suction fan 30, resulting in a problem such as increase in the distance (h0) by the distance (h1) accordingly. Furthermore, in the example of the arrangement shown in FIG. 9, since a portion including the light source 11 and the suction fan 30 protrudes to the wall surface side, a distance (h2) from the optical engine 10 to the projection light emitting position becomes longer as shown in FIG. 10, and there arises such a problem that the distance (h0) is increased accordingly.